This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-166433 filed on May 31, 2000.
1. Field of the Invention
The present invention relates to a fuel injection control system for an internal combustion engine, having the function of correcting a fuel injection amount during fuel injection.
2. Description of Related Art
A fuel injection control system for an internal combustion engine mounted on an electronically-controlled vehicle determines a requested injection amount in accordance with operating conditions before the start of injection. The system performs fuel injection by opening a fuel injection valve only for an injection time according to the requested injection amount to supply fuel of an amount corresponding to the requested injection amount to the internal combustion engine. However, the system has the following drawback. At the time of transient driving such as acceleration or deceleration, the operating conditions change from those at the time of determination of the required injection amount (before the start of injection). Thus, the fuel injection amount at the time of transient driving deviates from the proper fuel amount corresponding to the operating conditions during the fuel injection. As a result, the air-fuel (A/F) ratio at the time of transient driving deviates from a target A/F ratio, so that drivability is worsened, and exhaust emission is not reduced.
As disclosed in JP-A-63-9646, when acceleration is detected during fuel injection, a fuel injection amount is corrected so as to be increased according to the acceleration state.
JP-A-60-116840 discloses that the required injection amount is calculated a plurality of times per intake stroke at short intervals (intervals of 45xc2x0 CA(crank angle)), and the fuel injection is intermittently executed a plurality of times per intake stroke on the basis of the result of calculation.
However, JP-A-63-9646 has a drawback such that, since the fuel injection amount is corrected by being increased in expectation according to an acceleration state, the accuracy of the correction of increase at the time of acceleration deteriorates (the increase amount as the correction amount cannot be calculated with accuracy only on the basis of the accelerating state). Moreover, since the fuel injection amount is not corrected by being decreased at the time of deceleration, the fuel injection amount at the time of deceleration becomes excessive, and the A/F ratio is deviated to the rich side at the time of deceleration. The drawback is such that as the deceleration deteriorates the exhaust emission is not reduced.
In JP-A-60-116840, since the required injection amount is calculated a plurality of times per intake stroke, the time from the instance when the required injection amount is determined to the instance when the fuel injection is finished becomes shorter than that in a conventional method, so that the deviation of the fuel injection amount at the time of transient driving decreases. However, the fuel injection is performed with the required injection amount determined before the start of injection, so that the deviation of the fuel injection amount at the time of transient driving will not be solved perfectly.
An object of the present invention is to provide a fuel injection control system for an internal combustion engine, realizing improved fuel injection control accuracy (accuracy of the A/F ratio control) at the time of transient driving, and improved drivability and reduced exhaust emission at the time of transient driving.
According to the present invention, a fuel injection control system for an internal combustion engine calculates a required injection amount at an interval shorter than an injection interval by required injection amount calculating means. The control system executes fuel injection based on a required injection amount calculated just before start of the fuel injection when the fuel injection is executed by fuel injection control means. The control system calculates a required injection amount according to a driving state of the engine during the fuel injection. When a required injection amount of this time is different from that of last time, the control system extends or shortens a fuel injection time in accordance with the change amount. In the configuration, also in the fuel injection, the required injection amount according to the driving state is calculated and the fuel injection time is extended or shortened according to the change amount of the required injection amount. Thus, not only at the time of acceleration but also at the time of deceleration, the fuel injection amount can be properly corrected according to a change in the driving state. Thus, the A/F ratio at the time of transient driving can be controlled with accuracy, and improved drivability and reduced exhaust emission at the time of transient driving can be attained.